The female bonobo apes of the Wamba forest in the Democratic Republic of Congo had just finished breakfast and were preparing for a brief nap in the treetops, bending and crisscrossing leafy branches into comfortable day beds.

But one of the females was in estrus, her rump exceptionally pink and swollen, and four males in the group were too excited to sleep. They took turns wildly swinging and jumping around the fertile female and her bunkmates, shaking the branches, appearing to display their erections and perforating the air with high-pitched screams and hoots.

Suddenly, three older, high-ranking female bonobos bolted up from below, a furious blur of black fur and swinging limbs and, together with the female in estrus, flew straight for the offending males. The males scattered. The females pursued them. Tree boughs bounced and cracked. Screams on all sides grew deafening.

Three of the males escaped, but the females cornered and grabbed the fourth one — the resident alpha male. He was healthy, muscular and about 18 pounds heavier than any of his captors. But no matter.

The females bit into him as he howled and struggled to pull free. Finally, “he dropped from the tree and ran away, and he didn’t appear again for about three weeks,” said Nahoko Tokuyama, of the Primate Research Institute at Kyoto University in Japan, who witnessed the encounter. When the male returned, he kept to himself. Dr. Tokuyama noticed that the tip of one of his toes was gone.

“Being hated by females,” she said in an email interview, “is a big matter for male bonobos.”

The toe-trimming incident was extreme but not unique. Describing results from their long-term field work in the September issue of Animal Behaviour, Dr. Tokuyama and her colleague Takeshi Furuichi reported that the female bonobos of Wamba often banded together to fend off male aggression, and in patterns that defied the standard primate rule book.

Adult females responded to a broad range of male provocations — unwanted sexual overtures, food disputes, pushing, kicking, vocal threats, persistent pestiness — by forming coalitions of two or more females, who would then jointly take on their male tormentors.

Remarkably, the female partners in a bonobo posse cooperated with one another despite lacking any ties of blood or even close friendship. As the so-called dispersing sex, female bonobos must leave their birthplaces before puberty and find another social set to join, which means that none of the adult females in a given bonobo community are kin.

Moreover, female bonobos rarely formed coalitions with their preferred girlfriends — the individuals they spent the most time with and groomed the most ardently. Instead, the researchers found, coalitions arose when a senior female would step in and take the side of a younger peer caught up in an escalating conflict with a resident male.

By delivering the formidable luster of her social standing, as well as an extra pair of hands, the intervening senior pretty much guaranteed that the skirmish would break her way.

The new results add depth and complexity to our emerging understanding of Pan paniscus, the enigmatic, lithe great ape with the dark licorice eyes, who lives only in the Democratic Republic of Congo and is seriously endangered. The bonobo is a sister species to the more widespread common chimpanzee, Pan troglodytes, and the two share equal footing as our nearest primate kin.

Yet the apes have followed distinctly different behavioral paths. Chimpanzee society is male-dominated and features strong bonds between adult males and feeble ties between females.

In the bonobo world, by contrast, female camaraderie prevails, while the bonds between males are weak. “It’s a matriarchy,” said Amy Parish, a primatologist at the University of Southern California. “Females are running the show.”

The latest research indicates that the nature of the bonobos’ sororal bonds shifts depending on circumstances, and that the most effective deterrent to male harassment may be a cross-generational pact.

“I sometimes think that bonobos sit up late at night reading papers about primates, and then decide to do the opposite,” said Joan Silk, a primatologist at Arizona State University. “They’re unusual in so many ways.”

Bonobos are famed for their hypersexuality and the way they use sex as an all-purpose problem solver in every possible situation, permutation and combination. When bonobos come upon a great patch of fruit, for example, and tensions rise over feeding priority, the bonobos will decompress with a quick round of genito-genital rubbing and similar acts: males with females, males with males, females with females, juveniles with adults.

Female bonobos in Congo’s LuiKotale forest use specialized gestures and pantomime to convey their desire for a bit of girl-on-girl frottage, according to a report last year by Pamela Douglas and Liza Moscovice of the Max Planck Institute for Evolutionary Anthropology in Germany. The soliciting female will point backward with a foot toward her sexual swelling and then shimmy her hips in imitation of a rub, at which display the second bonobo will embrace her for the real thing.

“It’s status acknowledgment,” said Barbara Fruth, a bonobo researcher at the Royal Zoological Society in Antwerp, Belgium. “The approaching female is saying, ‘I know you’re higher-ranking than I am, I know you’re superior, but I would like to sit near you and maybe share your food.’”

Bonobos tongue-kiss, practice oral sex, have intercourse face-to-face, and make sex toys. Frances White, a biological anthropologist at the University of Oregon, once watched a female bonobo turn a stick into a kind of knobby “French tickler,” with which she then stimulated herself. “They’re not always family friendly,” Dr. White said.

Such erotic antics have earned bonobos a reputation as laid-back “hippie apes,” a label that researchers say belies the primate’s strategic intelligence and capacity for brutality. Dr. Parish, who studies bonobos in captivity, has seen the young offspring of dominant females flaunt their inherited power by marching over to lesser-ranking female adults, prying their jaws open and extracting the food from their mouths.

She also recounted the time that two females attacked a male at the Stuttgart Zoo in Germany and bit his penis in half. Fortunately, she said, “a microsurgeon at the zoo was able to repair the damage, and the male went on to reproduce.”

Nevertheless, bonobos are far less violent than chimpanzees, and female bonobos clearly benefit from life in a constructed sisterhood. Female chimpanzees cannot pick and choose a partner from among the available males, but must mate with all of them. Female bonobos can reject suitors without fearing for their lives. Infanticide is common among chimpanzees, but unheard-of among bonobos.

The outstanding question for researchers is how the female solidarity routine started.

Male chimpanzees remain in their natal home, so their male-male bonds are built on the standard evolutionary principle of kin selection. Female chimpanzees end up surrounded by nonrelatives in adulthood, so they mind their own business.

Why did female bonobos defy the norm and start cooperating with one another? And why don’t male bonobos forge alliances with other nearby males who are likely their brothers and cousins?

Differing ecological conditions may have helped set the stage for the behavioral divergence. By this hypothesis, bonobos evolved in a region with a comparatively abundant and reliable food source, which meant that females could forage in view of one another without coming to blows.

The more time they spent foraging, the more affiliative they became, and soon they were applying their displays of mutual respect and tolerance to other tasks, like rebuffing male harassers.

Chimpanzees evolved in drier climates, where food was scarce and foraging females had to compete with one another for limited goods. Who has time for friends?

As for male bonobos, they may be subordinate themselves to females in cliques, and they may have no interest in hanging out with the guys. But they have a secret social weapon: their mothers. Male bonobos stay with their mothers for life, and as her status grows with age, so does his.

Dr. White suggested that senior females cultivate relationships with younger females partly as a matchmaking gambit.

“The mother is finding partners for her son,” she said. “Why would a male bother harassing a female when he could have his mother do it for him?”

Researchers suggested that the new work has implications for understanding human evolution and the future, especially for women.

“We’re equally related to chimps and bonobos, and we have their entire range of behavioral variation available to us,” Dr. White said. “We can be as aggressive as the chimpanzee, or as female-allied as the bonobo.”

That female bonobos have found a path to “solidarity and sisterhood,” Dr. Parish said, “should give hope to the human feminist movement.”